The present invention is directed to a gauge having a magnetically driven pointer rotation device that is adapted to detect and indicate the position of a drive magnet coupled to a pressure sensing flexible diaphragm, and in particular a pointer rotation device including a power magnet that creates a magnetic circuit with the drive magnet.
Gauges, such as pressure gauges, include a flexible diaphragm that is located between a first fluid chamber and a second fluid chamber. A pointer assembly is often located in an indicator chamber of the gauge. The indicator chamber is separated from the fluid chambers by a separating wall that includes an aperture through which the pointer assembly is mechanically coupled to the diaphragm. In such a case, fluid within a fluid chamber is in contact with the pointer assembly. Mechanical or adhesive seals between the pointer assembly and the separating wall can be used, but the seals are prone to leakage and allow fluid to enter the indicator chamber. It is undesirable to have fluid come into contact with the pointer assembly as the fluid causes contamination of the pointer assembly and decreased operating efficiency.
A magnet coupled to the diaphragm has been provided in a fluid chamber for magnetic coupling to a helix attached to a pointer. A solid separating wall is provided between the magnet and the helix to separate the helix and pointer from the fluid chamber. However, the size of the air gap between the magnet and the helix must be relatively small and the air gap dimension must be closely controlled to avoid diminished accuracy in the pointer accurately reflecting the magnet position.